Im new to kiteboarding, and to save on equipment i plan on building the board myself. I have a lot of experience in r/c planes i.e. fiberglass and carbon . Since im limited to the types of foam I can find in my area, my question is whether it is possible to build a board with pink/blue foam core. You know i wont be pushing the board to its limits. Furthermore how much layers of fiberglass would be needed? From what i read, 3 layers of 6 oz fiberglass should do the job?

One more thing, a friend of mine has a cnc machine for cutting foam. Would that make a good board? To cut the desired shape on a cnc out of pink/blue foam, and strengthen it with couple layers of fiberglass?

You are used to foam, but for a beginner kiteboard, there is no need.
Do what this guy did instead, use birch or marine plywood if you want to be fancy, hardware store exterior grade if not:viewtopic.php?f=107&t=2375566
-faster build
-equivalent performance
-tough enough to take abuse

Foam board will be delicate, plus xps foam has the reputation of delaminating when the board heats up on beach , in car etc.
So I say go for wood.
But if you do glass over xps, I would go for 4 6oz layers rather than 3 with a >/+1/2" core, or it will be too delicate, a rock or your harness hook might hurt it..
Or if you must do foam, order structural foam online.
Pic of guy's ply board:

You can make a simple jig as in picture below.
make the pieces on the end stick up a bit higher (??15%, ?30%??) than your desired rocker if using 6mm ply, maybe 10-20% if using layers of <6mm ply.
place a little piece under the center as shown to prop up the center, making a concave.
screw down the edges in the middle of the rails to the base, forming the rocker and concave.
use little screws as needed elsewhere to assure good contact between layers.
If you want precise control of rocker/concave, use 3+ layers of 3mm ply.
If you glue up 2 layers at a time you can "tune" the results as you go with subsequent layers.
All at once is fine too though.

Actually by bending wood in that kind of shape you should have very little air inside, theoretically none.
Use epoxy, in my opinion it's worth the price.
Thicken it with a bit of cotton flock so it is like honey or molasses.
Apply it in a layer ~.5-1mm thick with a plastic saw tooth edged spatula/squeegee.
Screw parts together, or clamp them.
If you want to avoid epoxy, use gorilla glue, but it's equally a pain and the unused part usually hardens in the bottle.
There is a learning curve with epoxy, but it's not that bad, and with epoxy skills you can make or fix an awful lot of things. Lots of online resources.
If you want to avoid screw holes, you can do a similar jig but use 1x2 wood strips and long deck screws for the clamping, see below....

nafets wrote:you are telling me to screw the board to the building board?

Also, what if i use more layers of fiberglass on a pink/blue foam?

I see you have your heart set on home depot type extruded foam.

its relatively strong in compression for its density.
its also very brittle with little allowable strain.
which means if you flex it a lot, it will start to break down

as mentioned, many have had difficulties making long lasting bonds.
partly due to chemical adhesion to styrene and partly due to out-gassing of the blank over time.

so if you can deal with all of the above, you can make a cheap board with pink foam.

make the sandwich stiff (usually means a thick blank with lots of glass)
sand the blank with very coarse grit (60-80 min)
effectively design a "hollow" board wrapped around the foam (just dont bother to remove the foam.

some small test block will go a long way in deciding how much glass to resist compression and bending loads. (most likely 3 layer- 6oz for starters)

in the meantime, pick up a sheet of 1/2" A/C plywood
take a skill saw and rip out 3 or 4 test boards (in 10 min) to use while you decide on the final details of you sandwich creation.

the process is fun, both ways.
but remember that its not likely you will keep this board forever ( or even a season)
not only do you make mistakes and improve you build skillls.
you also improve your kiting skills and start looking at other designs.

My experiment with xps foam went as far as this:
cut out 1 foot square of ~1/2 inch xps, peel film off and rough up with 80grit sandpaper.
Apply 2 x 6oz e glass in epoxy to each side.
Cure.
pick up, flex, seems sort of stiff.
Flex harder, buckles in my hands.
Throw in trash.
I don't think it's very suitable, but I would say you would want to double up on the deck side if you use it.
plywood is a good start...
Look for used boards and used parts, or closeouts, (online etc.) or ask friends/kiters around...